Cracks due to resonances and vibration-induced fatigue can be halted. Drill
a small hole at the end of the crack (the end which
is propagating into the heart of the tubing) clear through the wall of the
aluminum. It is more difficult for a tear to continue to
develop past the hole. (This technique is often used in cymbals, where a
poor-quality casting can cause the outer edge of the
cymbal to crack due to fatigue. Works like a champ.)
Of course, one should immediately thereafter address the cause of the
original crack, which it sounds like you have done.
-- Eric K3NA
-----Original Message-----
From: cq-contest-bounces@contesting.com
[mailto:cq-contest-bounces@contesting.com]On Behalf Of Kristinn Andersen
Sent: 2004 August 5 15:32
To: cq-contest@contesting.com
Subject: [CQ-Contest] Aluminum fatigue cracks and scratches - treatment?
Hi:
I just noticed a mild scratch close to the base of my vertical aluminum pole
that serves as a vertical antenna and support for an inverted-V. This has
developed during the last year as a result of a friction against a steel
bolt close to the aluminum pole surface. It appears to be tolerable, as
long as it does not develop further - I have relocated that steel bolt and
the pole is guyed so bending/fatigue movements should be minimal at this
point.
Years back I had an aluminum vertical that initially had a relatively
"innocent" scratch at the base, which developed into a crack as the vertical
swayed with the wind, and the unit finally broke. A friend of mine advised
me afterwards that I could have prevented this fatigue development of the
scratch/crack by sanding and polishing it down so that there would be no
crack to propagate through the aluminum cross section. Now, I am thinking
about doing this, but would like to hear if any of you have a comment on
this. Sanding down the crack sure makes it disappear, but at the same time
I would be thinning the wall of the tube a little in this place. Any
comments?
73 de Kris, TF3KX
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